Conventional miniature threshold temperature electrical switches employing a meltable element which melts when the ambient temperature of the circuit breaker reaches a chosen value, to allow actuation of a spring means to break an interior electrical contact suffer from several disadvantages. One typical circuit breaker comprises two opposing springs, one stronger than the other, the stronger spring holding two electrical contacting members together. The stronger spring is typically supported on a meltable pellet having a melting point at the chosen temperature. An opposing and weaker spring attempts to force the contacts apart. At a given temperature, the pellet melts, thereby removing the strong spring's arresting force, whereupon the weaker spring forces the contacts apart.
Such opposing spring systems tend to be inherently vibration sensitive, since the switch elements of the breaker are held in contact by a balance of opposing springs with a substantial mass therebetween, typically in the form of a pressure plate. Under impact or acceleration conditions, the mass of the pressure plate can overcome the force of its associated spring to allow the contacts the momentarily disengage, thereby giving rise to unreliability to the fuse under sufficiently high vibration conditions. Thus, a useful contribution to the fuse art would be represented by a thermal fuse element which has substantially improved vibration resistance.
Another disadvantage of these prior circuit breakers is that because of the construction and arrangements of their parts, they do not lend themselves readily to completely automated mass manufacturing techniques. Also, it would reduce the cost and simplify their assembly if one rather than two springs were utilized.
Additionally, a breaker shoulder ideally be manufactured completely from components which can be readily made by elementary techniques, e.g. die forming, injection molding, wire forming, etc., in such configuration that no subassembly is necessary, and wherein the fuse can be assembled by a series of elementary inexpensive manufacturing operations. A fuse overcoming any and preferably all of the above shortcomings would constitute a novel and useful contribution to the art. The thermal fuse of the present invention is such a fuse.